The sealing devices of the known type have an axial-symmetrical “cup-shaped” form, which is centrally closed in applications intended for wheels which are non-driving and therefore do not have a shaft passing along the axis of the bearing, and laterally close the outer ring of the bearing, forming a static seal for protecting the bearing from any environmental contamination (water, mud, dirt, etc.).
In their more general form, the sealing devices comprise a screen, which is more or less cup-shaped, the screen being mounted on a collar of the outer ring of the rolling bearing by means of an interference force fit, and comprise in particular:
a cylindrical mounting wall, which is coaxial with an axis of symmetry of the bearing and which engages by means of the force fit with the collar of the outer ring of the bearing; and
an annular reading wall, which is transverse to the axis of symmetry and the cylindrical mounting wall, is rigidly connected to the cylindrical mounting wall and is arranged between a detection sensor mounted on the outside of the bearing and a phonic wheel mounted on an inner ring of the bearing, with which it defines a reading gap with given axial dimensions depending essentially on the positions of the phonic wheel and the screen, the thickness of the screen and the position of the detection sensor. The reading gap is normally designed to have extremely small axial dimensions so as to avoid reducing the capacity of a signal from the phonic wheel reaching correctly and in a clear and clean manner the detection sensor.
Analyzing the wear condition of both the screens and the phonic wheels it has been established that, owing to the dynamic action of the wheels connected to the wheel-hub units of motor vehicles, the inner ring of the bearing is subject to deflections which, in many cases, cause deviation of the phonic wheel which, precisely because of the small axial dimensions of the reading gap, accidently comes into contact with the annular reading wall of the screen.
Such accidental contact over time results in wear of the screen, in some cases negatively affecting the sealing capacity, as well as wear of the magnetized portion of the phonic wheel, causing a reduction of its emitted signal.